3 Answers
3

As far as I know, edibility (wow, I'm surprised that passes the spell checker!) is not a strictly defined term, biologically or otherwise. Humans have been around eating and drinking stuff long before the scientific method was around to study this question rigorously, and before there were regulatory agencies charged with approving new products as "safe." As one might imagine, knowledge of what is and is not edible was likely passed down by oral tradition and personal experience.

Honestly, I'm not even sure designating a food (or a substance) as edible or inedible really makes much sense. Let's consider wild fruit, as mentioned in your question. If ingesting 5 or more berries of hypothetical fruit X causes your body to have a nasty reaction, then we could probably agree that fruit X is toxic and inedible (even if eating only 1 or 2 berries might not elicit the same reaction). On the other hand, ingesting berries of hypothetical fruit Y causes no reaction unless consumed in much larger quantities (maybe 100 or more berries). Although fruit Y does cause a reaction when ingested in excessive amounts, it would be a stretch to call it inedible. This principle applies to many foods that we typically consider edible but can be unhealthy or even dangerous when taken in excess.

So where do we draw the line? How much of a substance do you have to ingest without an adverse reaction to deem it edible? I don't think there is an objective answer to this question. It is complicated further by the vast amounts of variation in the human population: food allergies, differences in tolerance to certain substances, etc.

+1: it has to be noted, though, that there is a very big difference between edibility and suitable for human consumption, where the second one is simply defined according to local regulation. A food that is suitable for human consumption for instance in Europe may not be suitable for human consumption in the US and vice versa (and many examples of this exist)
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nicoAug 28 '12 at 17:10

@nico Indeed. But whatever any arbitrary group (government, social organization, etc) decides to term as "suitable" does nothing to change the underlying biology, which was the original question (and should be considering the scope of this site). One would expect and hope that such policy decisions be based on the underlying biology...
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Daniel StandageAug 28 '12 at 17:31

1

surely I totally agree although, alas, these laws are seldom made by listening to scientist...
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nicoAug 28 '12 at 19:37

Much like Daniel Standage suggests, I think "edible" is more inferried than defined, sort of like looking at a black hole - its absence is defined by the activity around it. Human bodies are capable of metabolizing lots of compounds that become poisonous pass some threshold.

In medical terms there are LDmin and MLD and LD50: miminum Lethal Dose, Median Lethal Dose, Lethal Dose for 50% of the Population respectively.

There are also compounds that aren't lethal, but are definitely harmful. Trans-Fats are one, where the FDA hasn't determined any safe levels of Trans-Fats in foods; they're always dangerous and harm your system.

Then there are materials or chemicals that will simply pass through your system without being absorbed or interferring with anything. Cellulose (refined wood pulp) is a popular additive in pre-made diet foods because it adds mass and texture while being completely indigestable since humans do not produce cellulase. The same can be said for silicone dioxide (sand), which is also very unreactive and passes through your digestive system benignly.

So I'd say as long as whatever is eaten is below the LDmin and/or can benignly pass through your system without damage, it is 'edible.'

This is more a legal question, so I'll quote from what is lex in the EU:

Regulation (EC) No 178/2002 of the European Parliament and of the Council of 28 January 2002 laying down the general principles and requirements of food law, establishing the European Food Safety Authority and laying down procedures in matters of food safety

Article 2

Definition of "food"

For the purposes of this Regulation, "food" (or "foodstuff") means any
substance or product, whether processed, partially processed or
unprocessed, intended to be, or reasonably expected to be ingested by
humans.

"Food" includes drink, chewing gum and any substance, including water,
intentionally incorporated into the food during its manufacture,
preparation or treatment. It includes water after the point of
compliance as defined in Article 6 of Directive 98/83/EC and without
prejudice to the requirements of Directives 80/778/EEC and 98/83/EC.

"Food" shall not include:

(a) feed;

(b) live animals unless they are prepared for placing on the market
for human consumption;

(c) plants prior to harvesting;

(d) medicinal products within the meaning of Council Directives
65/65/EEC(21) and 92/73/EEC(22);

(e) cosmetics within the meaning of Council Directive 76/768/EEC(23);

(f) tobacco and tobacco products within the meaning of Council
Directive 89/622/EEC(24);

(g) narcotic or psychotropic substances within the meaning of the
United Nations Single Convention on Narcotic Drugs, 1961, and the
United Nations Convention on Psychotropic Substances, 1971;

So if we rely on the legal definition (well, that in Europe at least), then "reasonably expected to be ingested by humans" is about as much detail as we're going to get.
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Daniel StandageAug 28 '12 at 17:34

Indeed, but I tried to answer the intended question (as perceived by me, mind you) rather than the "edible definition" part. Anyway, the OP should probably look up "food safety" in the Wikipedia.
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rwstAug 28 '12 at 17:39